The invention relates to energy sources used for acquisition of seismic data of sub-surface formations.
To perform a field seismic survey of the earth""s sub-surface, a seismic energy source is used to generate a seismic signal (also referred to as a seismic pressure wave). The seismic signal is transmitted into the earth""s sub-surface, and a portion of the seismic signal is reflected back towards the surface of the earth where one or more detectors may be positioned to receive the reflected signal. The seismic data received is used to determine geophysical information about the earth""s sub-surface.
A typical energy source used for seismic acquisition includes dynamite that is exploded in a hole of some depth. For reliable performance, the dynamite may need to be placed in a relatively deep hole. In addition, multiple holes may be employed to create a pattern of seismic signals. Explosion of the dynamite creates expanding gas volume, downwardly moving shock waves as well as a substantial amount of lateral shock waves that are directed side ways. Useful data typically is derived from reflected signals of downwardly moving shock waves. The lateral shock waves from the energy source generate noise trains that frequently reduce the detector""s ability to see the reflected signal. Another disadvantage of using explosives such as dynamite as energy sources in seismic acquisition is that explosions may disrupt the environment around the survey site. With increased environmental protection concerns, use of such energy sources is generally not desirable, especially in environmentally sensitive areas.
Various types of alternative energy sources have been proposed or implemented. For example, use of air-gun energy sources as well as low frequency marine vibrators have been used. However, a need continues to exist for improved energy sources used in seismic acquisition systems.
In general, according to an embodiment, a seismic acquisition system includes an energy source having a perforating shaped charge to generate a seismic signal. A detector is positioned to detect a reflected signal in response to a seismic wavefront.
Other features and embodiments will become apparent from the following description and from the claims.